Nano-composite door facings, and related door assemblies and methods

ABSTRACT

A door skin adapted for construction of a door assembly is provided. The door skin is embodied as a rectangular solid sheet having interior and exterior opposing surfaces. The solid sheet contains a polymeric material and a nanocomponent. Also provided are door assemblies, and related methods.

CROSS-REFERENCE TO RELATED APPLICATION

The benefit of priority under 35 U.S.C. § 119(e) is claimed of U.S. Provisional Application No. 60/832,126 filed on Jul. 21, 2006, the complete disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed to door facings, door assemblies featuring at least one door facing, and methods of making the door facings and door assemblies.

BACKGROUND OF THE INVENTION

Doors are increasingly being manufactured from composite components containing plastic materials. Typical door assemblies comprise a pair of compression molded exterior skins, frequently having wood grain patterns on their outer surfaces. The door skins are mounted on a rectangular frame that separates and supports the skins in spaced relationship to one another. A hollow space between the skins typically is filled with an insulating structure, for example, cardboard, paper, fiberboard, or foam such as polyurethane.

Composite door assemblies provide several advantages over natural and steel doors. Composite door assemblies resist rot and corrosion experienced with solid wood and metal doors, respectively. The composite door assemblies also generally are better insulators than solid wood and metal doors. Because of material costs and manufacturing efficiencies, polymer composite door assemblies are considerably less expensive to manufacture than solid wood doors and can be designed to provide a reasonable facsimile of a wood grain door.

A typical compression molding process used in manufacturing available molded door-skins involves placing a predetermined weight of sheet molding compound (SMC) charge layers comprising a polymeric material and fiberglass reinforcement on a lower mold half. An upper mold half is then advanced into engagement with the lower mold half to force the SMC material to fill and to conform to the shape of the mold during compression. The mold halves are heated to about 150° C. to facilitate flow and cure the thermosetting reaction. Once solidified, the molded door skins are removed from the mold press. Often, the mold dies have contours and embossing features that imprint depressions, grooves, patterns, texture and the like into the molded door skin. The imprinted features often are configured as one or more square or rectangular depressions simulating the perimeter of one or more simulated panels. Alternatively, the facings may be flush.

Typically, sheet molding compounds contain a thermosetting resin system such as an unsaturated polyester resin (UPR) and an unsaturated co-curable reactive monomer, such as styrene (St). The sheet molding compounds also contain a reinforcing agent, such as glass fibers, often presented as 1 inch (2.54 cm) or half inch (1.27 cm) chopped fiberglass and/or a thin fiber mat. Additives commonly combined with sheet molding compounds include catalysts, activating agents, thickening agents, stabilizers, and inert fillers such as calcium carbonate, talc, and wood particles.

A problem that has been experienced with SMC compositions found in conventional compression molded door skins relates to shrinkage accompanying molding processes. Conventional SMC compositions have been found to undergo a high degree of polymerization shrinkage, estimated at about 7-10% in some cases. Shrinkage can cause severe surface quality and dimensional control problems in manufacturing.

Solutions have been offered for solving the shrinkage problem associated with conventional SMC compositions. One proposed solution involves the addition of thermoplastic polymers as low profile additives (LPA) to the SMC composition. The addition of large amounts of low profile additives, however, increases the material costs for manufacturing the door skins. Additionally, the addition of relatively large amounts of low profile additives has been found to sacrifice mechanical properties, such as tensile strength and impact resistance. Further, many low profile additives do not work well in low temperature processes, such as resin transfer molding, Seemann Composite Resin Infusion Molding Processes (SCRIMP), and hand lay-up/spray-up.

Another problem that has been experienced with SMC compositions found in some conventional compression molded door skins relates to their lack of dimensional stability, which may cause the door skins to shrink and expand in response to variations in temperature and humidity experienced with seasonal changes, or when used in combination with a glass storm door. For example, the surface temperature of the door facing behind a storm door may reach temperatures in excess of 82° C. (180° F.) in response to direct sunlight exposure. The surface temperature of a dark painted door behind a full view storm door can reach up to 116° C. (240° F.) in response to direct sunlight exposure. The interior door surface, on the other hand, is room temperature and therefore a substantial temperature differential may exist across the thickness of the door. Excessive dimensional instability can cause the door to bow or the door skin to delaminate from the peripheral frame in response to such temperature variations.

It has also been found that the dimensional instability of conventional door skins can adversely affect the smoothness and paintability of the door skin exterior surface. In some instances, depending upon the dimension instability and environmental conditions, the surface texture and/or paint finish of the door skin may become so blemished as to be aesthetically unacceptable to some consumers.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, a door facing adapted for construction of a door assembly is provided. The door facing features a rectangular solid sheet having first and second opposing surfaces. The solid sheet comprises a polymeric material and a nanocomponent.

According to a second aspect of the invention, a door assembly is provided featuring a frame and first and second door skins secured to opposite sides of the frame. At least one of the door skins comprising a rectangular solid sheet having interior and exterior surfaces. The solid sheet comprises a polymeric material and a nanocomponent.

A third aspect of the invention provides a method of forming a door skin, comprising the steps of providing a die mold having first and second dies defining a cavity, disposing a SMC charge layer comprising a polymeric material and a nanocomponent into the die mold, at least partially closing the die mold, shaping the polymeric material under pressure to establish a door skin, and removing the door skin from the die mold.

A fourth aspect of the invention provides a method for making a door assembly. According to this method, a door skin featuring a rectangular solid sheet having interior and exterior surfaces is attached to a frame. The sheet comprises a polymeric material and a nanocomponent dispersed in the polymeric material. A second door facing having the same or different characteristics is attached to the opposite side of the frame.

Other aspects of the invention are encompassed within the embodiments below, and include door skins, door assemblies, building structures feature a door assembly, and methods of making and using the same.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated in and constitute a part of the specification. The drawings, together with the general description given above and the detailed description of the preferred embodiments and methods given below, serve to explain the principles of the invention. In such drawings:

FIG. 1 is an elevated front view of an embodiment of a two-panel door in accordance with the invention; and

FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS AND PREFERRED METHODS OF THE INVENTION

Reference will now be made in detail to preferred embodiments and methods of the invention as illustrated in the accompanying drawings, in which like reference characters designate like or corresponding parts throughout the drawings. It should be noted, however, that the invention in its broader aspects is not limited to the specific details, representative devices and methods, and illustrative examples shown and described in this section in connection with the preferred embodiments and methods.

Referring more particularly to the illustrated embodiments, FIG. 1 depicts a door according to an embodiment of the invention generally designated by reference numeral 10. Door 10 may be an exterior entryway door or an interior passageway door of a building, such as a dwelling or commercial property. The mechanical properties that characterize embodiments of door 10 described herein make it particularly suitable for use as or in combination with a hurricane door. Exterior and passageway doors typically have a height of from about 6 foot, 8 inches to about 9 feet, more usually about 8 feet, and a width of about 3 to 4 feet, with 3 foot 6 inches being standard width for many passageway doors. Other uses of door 10 include furniture (e.g., cabinet, desk) drawers, furniture doors, and closet doors. Although not shown in the drawings, door 10 may include hardware, such as a handle, knob, or other grasping mechanism, with or without a locking mechanism. Door 10 may further include appropriate mounting hardware for its intended use, such as hinges for mounting door 10 to a wall structure (e.g., a building wall structure) or guide rails for allowing sliding movement of door 10. While the embodiments described herein relate primarily to doors, it should be understood that the disclosed invention is applicable for other composite decorative panels.

Door 10 includes front and rear door skins (also referred to herein and in the art as door facings) 12 and 14 parallel with one another. Either or both of door skins 12, 14 may be formulated to comprise the inventive door skin(s) of the present invention. Skin 12 has substantially planar interior and exterior surfaces bounded by perimeters. Likewise, skin 14 has substantially planar interior and exterior surfaces. Skins 12, 14 may have smooth or textured exterior surfaces, or a combination thereof. The texture may simulate that of a wood grain or other design. The coloration of skins 12, 14 is preferably a wood toned color, although any base coloration may be used. Stain, paint, or other dye may be applied to skins 12, 14, as may print ink grain designs and the like. Alternatively, an image can be printed on the exterior surfaces of door skins 12, 14, as described in U.S. Pat. No. 7,001,016. The aesthetic appearance and tactile feel of skins 12, 14 may be substantially identical to or different from one another. The exterior surfaces of door skins 12, 14 optionally may be sealed. Optionally, a veneer may be bonded to the exterior surfaces to provide a desired appearance (e.g., color, grain and/or inlay patterns of natural wood).

As shown in FIGS. 1 and 2, door skins 12, 14 are depicted as simulating multi-panel door surfaces. The illustrated embodiment contains two molded contoured regions 16, 18 that define and surround two panels 20, 22, respectively. A greater or lesser number of panels may be molded. Panels 20, 22 are preferably coplanar with one another. Each of the contoured regions 16, 18 is completely surrounded by a substantially planar main surface portion 24, so that contoured regions 16, 18 are integral with and interconnect main surface portion 24 with panels 20, 22, respectively. Optionally, panels 20, 22 lie in the same plane as main surface portion 24. Although skins 12, 14 are shown having identical multi-panel designs, it should be understood that skins 12, 14 may have different designs from one another and/or may be free of contours and panel-shaped designs.

Door skins 12, 14 are attached to opposite sides of peripheral frame or interior support structure 28. Mechanical fasteners or bonding adhesives may be used for attachment. Typically, a pair of parallel side members, known as stiles, establishes opposite side edges of door frame 28. A pair of parallel end members, known as rails, establishes the top and bottom edges of door frame 28. The frame members can be made of natural wood, man-made pressed wood, or any other suitable material.

Door assembly 10 also optionally includes a core component disposed between skins 12, 14. Core component may comprise a foam formed of any suitable polymer material which can be injected and formed in place between skins 12, 14, or can be pre-formed and then placed between door skins 12, 14 and surrounded by frame 28. Other non-foam materials that may be used include, for example, corrugated pads and other insulation and materials. It should be noted that door skins 12, 14 may be adhered to the core. Optionally, door assembly 10 may be produced without a core, e.g., to maintain an empty hollow area between skins 12, 14.

Door skins 12, 14 may be made of various resins systems and additives compatible with the present invention, including those materials commonly employed in the door-fabrication industry. According to a preferred embodiment, door skins 12, 14 are made of a thermosetting resin, preferably a sheet molding compound (SMC) or bulk molding compound (BMC) composition. The thermosetting composition preferably comprises an unsaturated polyester resin and an unsaturated, co-curable crosslinking monomer such as styrene reactive with the polyester. Typically, a heat-activated catalyst is included in the composition. Another example of a suitable thermosetting resin is a polyurethane resin, such as a urethane sheet molding compound, which may comprise, for example, a urethane polymer or prepolymer, a crosslinker and/or linking agent, such as a di- or polyisocyanate, and a catalyst. Other thermosetting and thermoplastic resin systems can be used in addition to or as alternatives for the unsaturated polyester, such as phenolic resins, vinyl ester resins, and epoxy resins. Additionally, various olefin homopolymers, copolymers, and terpolymers may also be included, such as polyethylene, polypropylene, polystyrene, acrylonitrile-butadiene-styrene (ABS), acrylate-styrene-acrylonitrile (ASA), and others. The unsaturated polyester resin may comprise a polycondensation reaction product of one or more dihydric alcohols and one or more unsaturated polycarboxylic acids.

Nanocomponents that may be selected for use in the compositions and methods of the invention include inorganic clays such as montmorillonite, vermiculite, illite minerals such as ledikite, layered double hydroxides or mixed metal hydroxides, and others. Inorganic clays such as montmorillonite preferably have crystalline layers that are highly anisotropic, often possessing a platelet thickness on the order of about 1 Å to about 50 Å, such as about 10 Å (1 nm). Platelet spacing may be determined using X-ray diffraction. The lateral dimensions of the nanocomponent are not particularly limited, but generally are advantageously within a range of about 30 nm to about 10 micron. Further description of nanocomponents and methods of making the same may be found in U.S. Pat. Nos. 6,849,680 and 5,780,376, incorporated herein by reference.

Inorganic clays and certain other nanocomponents are hydrophilic in nature, but can be organically modified to become compatible with the organic polymer matrix. Preferably, modification involves intercalation of the clay mineral platelets. The platelets may be intercalated by ion exchange using, for example, cations such as ammonium cations (e.g., alkylammonium cations), or reactive organosilane compounds that cause the multi-lamellar or layered particles to delaminate or swell.

The ion-exchange technique may involve first “swelling” the clay with water or some other polar solvent, and then treating the clay with the intercalating agent. The function of the intercalating agent is to increase the “d-spacing” between the layers of the inorganic clay. The organophilic clay is then isolated and dried.

The nanocomponents alternatively may be treated with a monomer or resin that facilitates intercalation, and an intercalating agent (e.g., quaternary ammonium salt). Examples of monomers and resins for treating the nanocomponents include acrylic monomers, styrene, vinyl monomers, isocyanates, polyamides, polyamines, phenolic resins, polyamide resins, epoxy resins, polyfunctional amines, and unsaturated polyester resins. The intercalating agent may be selected to match the structure of the resin and have functional groups that are reactive with the resin.

The amount of intercalating agent may range from 5-50 weight percent of the clay, depending upon the desired properties. Greater proportions of intercalating agent improve clay dispersion, which can improve mechanical properties but also increase viscosity. A discussion of intercalating agents is found in U.S. Pat. No. 6,974,848, which is incorporated herein by reference for its disclosures of inorganic clays, intercalating techniques and intercalating agents.

Commercial products containing montmorillonite modified with a quaternary salts include Cloisite® 10, Cloisite® 20, Choisite® 15A, Cloisite® 25A, Clisite® 30B, Cloisite® 93A, and Cloistie® Na⁺, each of which includes at least one hydrogenated tallow or tallow moiety in the quaternary salt. The Cloisite® products are available through Southern Clay products of Gonzales, Tex., a subsidiary of Rockwood Specialties, Inc.

The composition may include additional components, such as low shrinkage and low profile additives, organic initiators (e.g., tertiary-butyl peroxybenzoate), thickening agents (e.g., oxides, hydroxides, and alcolates of magnesium, calcium, aluminum), stabilizers or inhibitors, fillers, reinforcements, and other additives.

Low profile additives have been defined as relatively polar thermoplastic polymeric materials believed to encourage the formation of microvoids in sheet molding compositions. It is believed that low profile additives are at least partially immiscible with an unsaturated polyester resin system, so that compression molding and setting of sheet molding compositions containing low profile additives is accompanied by the formation of a multi-phasic polymer system. Examples of low profile additives include thermoplastic polymers, such as saturated polyesters, polystyrene, polyvinyl acetate, and copolymers and terpolymers of the same. Other low profile additives known in the art may also be included. It is believed that the nanocomponents improve the effectiveness of low profile additives, and may reduce or eliminate the need for low profile additives.

Fillers and reinforcements may serve various purposes, including extending the resin, improving mold flow, and/or imparting desired characteristics and mechanical properties to the finished product. Examples of fillers include calcium carbonate, clay, graphite, magnesium carbonate, talc, and mica. Examples of reinforcements include fiberglass, graphite, aramides, and cellulosic materials, such as wood fibers, sawdust, straw, etc. Fiberglass is often found in many commercial sheet molding compounds, and often is present as 1 inch or half inch chopped fiberglass. The filler and reinforcement materials may take various physical shapes, such as fibrous, microspheres, or one or more mats. Other additives that may be used include, for example, mold release agents, shelf inhibitors, wetting agents, homogenizers, UV retardants, pigments, fire retardants, mold-release agents, and/or thickening agents.

The SMC composition may be embodied to constitute, for example, about 15 to about 25 weight percent of the thermosetting resin system, about 10 to about 20 weight percent low profile additive, about 1 to about 5 weight percent nanocomponent, and 13 to about 20 weight percent reinforcement, and about 30 to about 50 weight percent filler, and optionally other ingredients. Concentrations may be adjusted within and outside of these ranges as warranted for obtaining desired properties. An exemplary composition is set forth in the Table below:

TABLE Component Weight Percent Unsaturated polyester 16.0 Low profile & shrinkage additives 11 Nanocomponent 3.0 Catalyst 0.5 Inhibitor 0.2 Thickener 0.5 Pigment 1.7 Compatibilizer 0.8 Zn Stearate 0.9 Calcium carbonate 48.0 Fiberglass 17.4

According to an embodiment for preparing the composition, the resin (e.g., unsaturated polyester), reactive monomer (e.g., styrene), low profile additive, and nanocomponents, are pre-blended together. Blending may be accomplished, for example, by high speed agitation for about 30 minutes. The fillers, additives, and/or other components are then added to the blend and mixed to form a paste. The SMC paste is combined on an SMC machine with a chopped fiberglass roving (e.g., 1 inch (2.54 cm) or 0.5 inch (1.27 cm)). Other sequences for combining and blending these and other components are contemplated. It is within the scope of the invention to introduce one or more of the composition ingredients to the molding die as separate components, i.e., without pre-blending.

Any suitable molding technique may be employed for compressing and shaping door skins 12, 14, including, for example, compression molding, resin transfer molding, injection compression, thermoforming, and injection molding. Generally, compression molding comprises introducing the pre-blend and/or unblended components onto a lower die, the moving one or both dies towards the other to form a closed cavity. The dies may possess embossing structures and texture designed to transfer embossments and grain to the molded door, as is known in the art. During pressing, the components are pressed together between the upper and lower dies and shaped by application of heat and pressure. Sheet molding compounds are often pressed within a temperature range of about 135° C. (275° F.) to about 177° C. (350° F.), more preferably about 138° C. (280° F.) to about 160° C. (320° F.). The dies exert a pressure on the composition of, for example, about 1000 to about 2000 psi. The pressing operation may last, for example, about 30 seconds to 2 minutes.

During compression, the polymeric material is softened and caused to flow throughout the mold cavity created by the dies. In the event that a thermoset polymer system is selected, the polymeric material cures into a set shape. The pressed door skin is then removed from the mold.

Without wishing to be bound by any theory, it is believed that the addition of nanocomponents can reduce the amount of shrinkage occurring in the SMC composition to provide low or zero shrinkage compositions. In conventional sheet molding compound compositions the unsaturated polyester (UP) reacts with styrene (St) during cure and separates from the low profile additive (LPA), resulting in a UP-rich phase and an LPA-rich phase. The UP-rich phase experiences volume shrinkage, whereas stress-induced microcracking occurs in the LPA-rich phase or at the interface of the phases to create microvoids to cause a volume increase. However, the UP-rich phase experiences a much faster reaction rate than the LPA-rich phase. As a consequence, the UP-rich phase shrinks and sets before the LPA-rich phase is able to form microvoids.

The incorporation of nanocomponents into the inventive formulation is believed to increase the reaction rate in the LPA-rich phase and earlier onset of critical modulus for microcracking due to the presence of nanocomponent in the LPA-rich phase. Therefore, the nanoncomponents cause earlier microvoid formation and volume expansion, leading to better shrinkage control and improved composite surface quality.

The lower or zero shrinkage in turn enhances the composite surface quality and adhesion between the composite surface and paint of the composite. Additionally, the presence of the nanocomponents and other fillers (e.g., calcium carbonate) imparts improved toughness and tensile module to the composite without sacrificing tensile strength. It is also believed that the nanocomposites improve barrier properties of the composite, and provide greater dimensional stability in response to weather changes.

Finally, the use of nanocomponents lowers the density of the molded article due to microvoid generation, preferably to a range of about 1.5 to 1.7 g/cm³, compared to a density of 1.75 to 1.80 g/cm³ for a comparable system free of nanocomponents. As a consequence, less material usage and reduced weights are attained.

The foregoing detailed description of the certain preferred embodiments of the invention has been provided for the purpose of explaining the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated. This description is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Modifications and equivalents will be apparent to practitioners skilled in this art and are encompassed within the spirit and scope of the appended claims and their appropriate equivalents. 

1. A door skin adapted for construction of a door assembly, comprising: a rectangular solid sheet having interior and exterior opposing surfaces, the solid sheet comprising a polymeric material and a nanocomponent.
 2. The door skin of claim 1, wherein the polymeric material comprises a reaction product of an unsaturated polyester and a co-curable unsaturated monomer.
 3. The door skin of claim 2, wherein said sheet molding compound comprises at least about 10% by weight chopped fiberglass.
 4. The door skin of claim 2, wherein the sheet further comprises calcium carbonate filler and peroxide catalyst.
 5. The door skin of claim 1, wherein the sheet further comprises a low profile additive.
 6. The door skin of claim 1, wherein the exterior surface includes contoured portions simulating door panels.
 7. The door skin of claim 1, wherein said exterior surface has a wood grain texture.
 8. The door skin of claim 1, wherein the nanocomponent comprises an intercalated, modified clay mineral.
 9. The door skin of claim 8, wherein the intercalated, modified clay mineral comprises montmorillonite.
 10. The door skin of claim 9, wherein the intercalated, modified clay mineral further comprises a quaternary ammonium salt as a modifier.
 11. A door assembly, comprising: a frame; and first and second door skins secured to opposing sides of said frame, at least one of the door skins comprising a rectangular solid sheet having first and second opposing surfaces, the solid sheet comprising a polymeric material and a nanocomponent.
 12. The door assembly of claim 11, wherein the polymeric material comprises a reaction product of an unsaturated polyester and a co-curable unsaturated monomer.
 13. The door assembly of claim 12, wherein said sheet molding compound includes at least about 10% by weight chopped fiberglass.
 14. The door assembly of claim 12, wherein the solid sheet further comprises calcium carbonate filler and peroxide catalyst.
 15. The door assembly of claim 11, wherein the solid sheet further comprises a low profile additive.
 16. The door assembly of claim 11, wherein the exterior surface includes contoured portions simulating door panels.
 17. The door assembly of claim 11, wherein said exterior surface has a wood grain texture.
 18. The door assembly of claim 11, wherein the nanocomponent comprises an intercalated, modified clay mineral.
 19. The door assembly of claim 18, wherein the intercalated, modified clay mineral comprises montmorillonite.
 20. The door assembly of claim 19, wherein the intercalated, modified clay mineral further comprises a quaternary ammonium salt as a modifier.
 21. A method of forming a door skin, comprising: providing a die mold having first and second dies defining a cavity; disposing a SMC charge layer comprising a polymeric material, and a nanocomponent into the die mold; closing the die mold and curing the polymeric material under pressure to establish a door skin; and solidifying and removing the door skin from the die mold.
 22. A method of forming a door assembly, comprising: providing a die mold having first and second dies defining a cavity; disposing a SMC charge layer comprising a polymeric material and a nanocomponent into the die mold; closing the die mold and curing the polymeric material under pressure to establish a door skin; removing the door skin from the die mold; and attaching the door skin to a door frame. 